1. Field of Invention
This invention relates to an electro-optical sensing device for detecting the presence or concentration of an analyte in a liquid or gaseous medium. More particularly, the invention relates to a fluorescence sensing device which is characterized by a compact size, high sensitivity and high signal-to-noise ratios.
2. Background Art
U.S. Pat. No. 5,517,313, the disclosure of which is incorporated herein by reference, describes a fluorescence sensing device comprising a layered array of a fluorescent indicator molecule-containing matrix (hereafter, "fluorescent matrix"), a high-pass filter and a photodetector. In this device, a light source, preferably a light-emitting diode ("LED"), is located at least partially within the fluorescent matrix, such that incident light from the light source causes the indicator molecules to fluoresce. The high-pass filter allows emitted light to reach the photodetector, while filtering out scattered incident light from the light source.
The fluorescence of the indicator molecules employed in the device described in U.S. Pat. No. 5,517,313 is modulated, e.g., attenuated or enhanced by the local presence of the analyte. For example, the orange-red fluorescence of the complex, tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) perchlorate is quenched by the local presence of oxygen. This complex can, therefore, advantageously be used as the indicator molecule of an oxygen sensor. Similarly, other indicator molecules whose fluorescence is affected by specific analytes are known.
In the sensor described in U.S. Pat. No. 5,517,313, the fluorescent matrix is permeable to the analyte. Thus, the analyte can diffuse into the fluorescent matrix from the surrounding test medium, thereby affecting the fluorescence emitted by the indicator molecules. The light source, fluorescent matrix, high-pass filter and photodetector are configured such that at least a portion of the fluorescence emitted by the indicator molecules impacts the photodetector, generating an electrical signal which is indicative of the concentration of the analyte in the surrounding medium.
While the sensing device described in U.S. Pat. No. 5,517,313 represents a marked improvement over prior art devices, there remains a need for sensors that are even more compact and which have superior sensing characteristics than those described therein. Thus, it is an object of the present invention to provide an improvement to the sensing devices described in the aforementioned patent.